The present invention relates to a photosensor such as a photoelectric transducer element in which hydrogenated amorphous silicon is used and a one-dimensional image sensor in which the photoelectric transducer is used.
As a one-dimensional image sensor in which hydrogenated amorphous silicon is used, a photoelectric transducer element having a structure of metal/a--Si:H/ITO (Indium Tin Oxide) such as that described in Japanese Patent Laid-Open No. 84457/1983 is often utilized. Such a photoelectric transducer element is shown in FIG. 1. Hydrogenated amorphous silicon is usually indicated by a--Si:H, as described above. In FIG. 1, the reference numeral 1 denotes an insulating substrate, 2 a metal electrode, 3 a hydrogenated amorphous silicon film obtained by the glow discharge decomposition of SiH.sub.4 gas, and 4 an ITO electrode. Indium tin oxide is transparent, and the ITO electrode 4 is therefore transparent. Although a photoelectric transducer element having this structure has good properties, it is necessary to form a transparent protective film 5 on the photoelectric transducer element, as shown in FIG. 2, when it is practically used. Si.sub.3 N.sub.4, SiO.sub.2 and the like are commonly used for the protective film. It has been found, however, when the protective film is actually formed on the above-described photoelectric transducer element, the properties are greatly deteriorated, as shown in FIG. 3. FIG. 3 shows the properties in the dark of the photoelectric transducer element having the structure shown in FIG. 1. FIG. 3 shows the reverse current which flows when the voltage which is ordinarily applied to ITO, namely, a voltage of 0 to 7 V is applied to the ITO electrode of the negative polarity. In an ordinary one-dimensional image sensor, the reverse current is preferably at most 10.sup.-9 A/cm.sup.2. The line l.sub.1 in FIG. 3 shows the property before the formation of the protective film, the property being very good. On the other hand, when an Si.sub.3 N.sub.4 film or SiO.sub.2 film is formed, the property becomes degraded by more than 1,000 times, as indicated by the line l.sub.2. This degraded property precludes the utility of the photoelectric transducer element. The degradation of the property is considered to be because the junction property of the interface between the a--Si and ITO is deteriorated due to the formation of an Si.sub.3 N.sub.4 or SiO.sub.2 film.